Inline If-Else Statement Based on Macro Argument

Question

How do I do an inline if-else statement?

\draw[draw = #1, fill = \if black#1 white \else black \fi, line width = 0.1mm]
  (#2, #3) circle [radius = 0.25cm];

I've tried to do it based on this answer, for example, but with no success:

\begingroup
  \def\color{#1}
  \def\black{black}
\draw[draw = #1, fill = \ifx\color\black white \else black \fi, line width = 0.1mm]
    (#2, #3) circle [radius = 0.25cm]; % chktex 1
\endgroup

I did try many other methods but none seem to work.

Here is a minimal complete example:

\documentclass{article}
\usepackage{tikz}
% Parameters
%
% 1: dimension (in cm)
% 2: board size (square)
% 
% Example: A 19x19 board with size 10cm x 10cm: `\gogrid{10}{19}'
\newcommand{\goGrid}[2]{
  \pgfmathsetmacro{\step}{#1 / (#2 - 1)} % chktex 1
\draw[step=\step] (0, 0) grid (#1, #1);
}
\newcommand{\drawStone}[3]{
  \draw[draw = #1, fill = \if black#1 white \else black \fi, line width = 0.1mm]
    (#2, #3) circle [radius = 0.25cm];
}
\begin{document}
  \begin{tikzpicture}
    \goGrid{10}{19}
\drawStone{white}{2 * 10cm / 18}{3 * 10cm / 18}

\end{tikzpicture}
\end{document}

(Why are there dozens of ways of doing if statements in TeX but all of them seem super finicky? T.T)

Answer 1

You can borrow a conditional from the L3 layer:

\documentclass{article}
\usepackage{tikz}
% Parameters
%
% 1: dimension (in cm)
% 2: board size (square)
% 
% Example: A 19x19 board with size 10cm x 10cm: `\gogrid{10}{19}'
\newcommand{\goGrid}[2]{
  \pgfmathsetmacro{\step}{#1 / (#2 - 1)} % chktex 1
\draw[step=\step] (0, 0) grid (#1, #1);
}
\ExplSyntaxOn
\cs_new_eq:NN \myIfStrEqTF \str_if_eq:nnTF
\ExplSyntaxOff
\newcommand{\drawStone}[3]{
  \draw[draw = #1, fill = \myIfStrEqTF{black}{#1}{white}{black}, line width = 0.1mm]
    (#2, #3) circle [radius = 0.25cm];
}
\begin{document}
  \begin{tikzpicture}
    \goGrid{10}{19}
\drawStone{white}{2 * 10cm / 18}{3 * 10cm / 18}

\end{tikzpicture}
\end{document}

Answer 2

Much simpler: -black is white and conversely.

\documentclass{article}
\usepackage{tikz}
% Parameters
%
% 1: dimension (in cm)
% 2: board size (square)
%
% Example: A 19x19 board with size 10cm x 10cm: `\gogrid{10}{19}'
\newcommand{\goGrid}[2]{%
  \pgfmathsetmacro{\step}{#1 / (#2 - 1)} % chktex 1
  \draw[step=\step] (0, 0) grid (#1, #1);%
}
\newcommand{\drawStone}[3]{% -#1 is the complementary color
  \draw[draw = #1, fill = -#1, line width = 0.1mm]
    (#2\step, #3\step) circle [radius = 0.25cm];
}
\begin{document}
  \begin{tikzpicture}
    \goGrid{10}{19}
    \drawStone{white}{2}{3}
    \drawStone{black}{4}{5}
  \end{tikzpicture}
\end{document}

I also simplified \drawStone.

Answer 3

A more cumbersome way of doing the trick where not so many new things are used could be:

\documentclass{article}
\usepackage{tikz}
% Parameters
%
% 1: dimension (in cm)
% 2: board size (square)
% 
% Example: A 19x19 board with size 10cm x 10cm: `\gogrid{10}{19}'
\newcommand{\goGrid}[2]{
  \pgfmathsetmacro{\step}{#1 / (#2 - 1)} % chktex 1
\draw[step=\step] (0, 0) grid (#1, #1);
}
% Paraphernalia ;-)
\newcommand\Exchange[2]{#2#1}%
\newcommand\FirstOfTwo[2]{#1}%
\newcommand\SecondOfTwo[2]{#2}%
\newcommand{\drawStone}[3]{%
  \begingroup
  \edef\tempa{\unexpanded{#1}}%
  \def\tempb{black}%
  \expandafter\endgroup
  \ifx\tempa\tempb\expandafter\FirstOfTwo\else\expandafter\SecondOfTwo\fi
  {\Exchange{white}}%
  {\Exchange{black}}%
  {\draw[draw = #1, fill = }, line width = 0.1mm]
    (#2, #3) circle [radius = 0.25cm];
}
\begin{document}
  \begin{tikzpicture}
    \goGrid{10}{19}
\drawStone{white}{2 * 10cm / 18}{3 * 10cm / 18}

\end{tikzpicture}
\end{document}

(Why are there dozens of ways of doing if statements in TeX but all of them seem super finicky? T.T)

They seem super finicky because the programming paradigm of the typesetting language TeX is different from the programming paradigms of most programming languages people are used to.

When learning TeX/LaTeX, don't try to transfer knowledge about programming in other languages (e.g., C++ or Java or Scheme) to TeX/LaTeX at too early a learning stage.
At the beginnings stick to the terminology introduced in Donald E. Knuth's TeXbook. That terminology is brought up because the concepts underlying TeX differ and thus their description/explanation requires different vocabulary.
The transfer of knowledge about programming in other languages can be done when you know how TeX works and thus know how to do the transfer properly.
E.g., you need to get familiar with concepts like "token"/"tokenization" and "expansion". And you need to get familiar with the fact that in TeX different levels of execution are intertwined - a fact which in the TeXbook is brought to the attention of learners by means of an analogy where the program TeX is seen as a beast which has eyes and a digestive tract with different stages of digestion (mouth, gullet, stomach, ...).

Answer 4

You don't really need a test here, just select the complementary color

\documentclass{article}
\usepackage{tikz}
\newcommand\notwhite{black}
\newcommand\notblack{white}
% Parameters
%
% 1: dimension (in cm)
% 2: board size (square)
% 
% Example: A 19x19 board with size 10cm x 10cm: `\gogrid{10}{19}'
\newcommand{\goGrid}[2]{%
  \pgfmathsetmacro{\step}{#1 / (#2 - 1)} % chktex 1
%
  \draw[step=\step] (0, 0) grid (#1, #1);%
}
\newcommand{\drawStone}[3]{%
  \draw[draw = #1, fill = \UseName{not#1}, line width = 0.1mm]
    (#2, #3) circle [radius = 0.25cm];
}
\begin{document}
  \begin{tikzpicture}
    \goGrid{10}{19}
\drawStone{white}{2 * 10cm / 18}{3 * 10cm / 18}

\end{tikzpicture}
\end{document}